1. Field of the Invention
The present invention relates to a dynamic pressure bearing having an axial bearing surface formed with dynamic pressure generating grooves, and a method of manufacturing the same.
2. Description of the Prior Art
Hitherto, a dynamic pressure bearing of this type has been known such that, as shown in FIG. 3, an axial bearing surface 51 has dynamic pressure generating grooves 52, 52 . . . formed thereon by press working of the axial bearing surface 51.
The dynamic pressure generating grooves 52, 52 . . . formed simply by press working have a drawback that each ridge portion 53 defined between the adjacent dynamic pressure generating grooves 52, 52 is tapered toward a direction in which it projects and, in addition, a projecting end or top end 53A of the ridge portion 53 is rounded all over so that the top end 53A which is to function as a bearing surface is not flat. Therefore, there occurs a problem that the dynamic pressure generating grooves 52 could only generate a small dynamic pressure, which results in a small load-carrying capacity.
Another type of dynamic pressure bearing is known such that, as shown in FIG. 2A, an axial bearing surface 61 has dynamic pressure generating grooves 62, 62 . . . formed thereon by etching being effected with the axial bearing surface 61. In this case, a top end 63A of a ridge portion 63 defined between the adjacent grooves 62 and 62 is not rounded or arcuately curved all over and contains a larger flat surface area than in the case of the first mentioned type of dynamic pressure bearing. This type of dynamic pressure bearing, therefore, can provide a larger load-carrying capacity than does the former type of dynamic pressure bearing.
In this instance, however, as shown in FIG. 2A, a projection 65 is likely to be formed on an edge portion of the top end 63A of the ridge portion 63 as a result of above mentioned etching. There occurs a problem that such a projection 65 may damage an opposite surface.
With a view to solving this problem, it may be conceived that each ridge portion 63 as shown in FIG. 2A is subjected to lapping, the top end 63A of the ridge portion 63 being then subjected to abrasion. By this treatment it is possible to eliminate such projection 65 present on the top end 63A of the ridge portion 63 as shown in FIG. 2B. However, the fact that the top end 63A is arcuately curved as a whole involves a problem that the load-carrying capacity is substantially reduced.